Magnetic tape cartridge

ABSTRACT

A magnetic tape cartridge includes a cartridge casing and a single reel which is contained in the cartridge casing for rotation. The reel has a reel hub in the form of a cylindrical member which has a bottom wall and is provided with an opening and a stopper gear formed on the bottom wall. A brake member is provided with a brake gear and is movable up and down between an operative position where the brake gear is brought into engagement with the stopper gear to prevent rotation of the reel and a retracted position where the brake gear is disengaged from the stopper gear to permit rotation of the reel. The brake member is normally urged toward the operative position and moved to the retracted position by a pusher member of a tape drive system which acts on the brake member through the opening in the reel hub when the magnetic tape cartridge is loaded in the tape drive system. A continuous wall portion is erected around the opening in the reel hub, and the brake member includes a horizontal portion and a continuous skirt portion which extends downward from the horizontal portion and is in contact with the continuous wall portion of the reel hub to close the opening together with the horizontal portion. The brake member is moved between the operative position and the retracted position with the skirt portion kept in cotact with the continuous wall portion of the reel hub.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a magnetic tape cartridge, and moreparticularly to a magnetic tape cartridge comprising a cartridge casingand a single reel around which a magnetic tape is wound and which iscontained in the cartridge casing for rotation.

[0003] 2. Description of the Related Art

[0004] There has been known a single reel magnetic tape cartridge,comprising a cartridge casing and a single reel around which a magnetictape is wound and which is contained in the cartridge casing forrotation, as a recording medium for an external storage for a computerand the like. Such a single reel magnetic tape cartridge is used forretaining important data of a computer or the like and accordingly isarranged so that trouble such as tape jamming does not occur and themagnetic tape is not accidentally drawn out.

[0005] The reel is provided with a cylindrical reel hub having a closedbottom and stopper gear teeth are formed in a circle and a brake memberprovided with a brake gear which is adapted to be brought intoengagement with the stopper gear teeth is disposed to be movable in thedirection of thickness of the cartridge casing along the axis ofrotation of the reel. The brake member is urged, for instance, by acoiled spring toward a position where the stopper gear teeth are engagedwith the break gear to prevent rotation of the reel when the magnetictape cartridge is not used. When the magnetic tape cartridge is loadedin a recording and reproducing system, a brake release spindle of therecording and reproducing system pushes upward the brake member todisengage the stopper gear teeth from the brake gear.

[0006] However if a space is formed between the brake member and thereel hub when the brake member is moved upward, dust and dirt can enterthe inside of the cartridge casing through the space.

SUMMARY OF THE INVENTION

[0007] In view of the foregoing observations and description, theprimary object of the present invention is to provide a magnetic tapecartridge in which dust and dirt can be prevented from entering theinside of the cartridge casing when the brake member is moved upward topermit rotation of the reel.

[0008] In accordance with the present invention, there is provided amagnetic tape cartridge comprising a cartridge casing, a single reelaround which a magnetic tape is wound and which is contained in thecartridge casing for rotation, the reel having a reel hub in the form ofa cylindrical member which has a bottom wall and is provided with anopening and a stopper gear formed on the bottom wall, and a brake memberwhich is provided with a brake gear and is movable up and down betweenan operative position where the brake gear is brought into engagementwith the stopper gear to prevent rotation of the reel and a retractedposition where the brake gear is disengaged from the stopper gear topermit rotation of the reel, the brake member being normally urgedtoward the operative position and moved to the retracted position by apusher member of a tape drive system which acts on the brake memberthrough the opening in the reel hub when the magnetic tape cartridge isloaded in the tape drive system,

[0009] wherein the improvement comprises that

[0010] a continuous wall portion is erected around the opening in thereel hub, and

[0011] the brake member comprises a horizontal portion which is disposedabove the opening in the reel hub and receives force from the pushermember when the brake member is moved to the retracted position and acontinuous skirt portion which extends downward from the horizontalportion and is in contact with the continuous wall portion of the reelhub, thereby closing the opening together with the horizontal portion,the brake member being moved between the operative position and theretracted position with the skirt portion kept in contact with thecontinuous wall portion of the reel hub.

[0012] It is preferred that the brake member comprises a first memberand a second member which abuts against the first member from above andis movable up and down together with the first member, said horizontalportion and the skirt portion are formed on the first member and thebrake member is urged toward the operative position by a spring meanswhich acts on the second member.

[0013] The skirt portion may be fitted either on or in the continuouswall portion.

[0014] In the case where the brake member comprises the first and secondmembers, it is preferred that the first and second members abut againsteach other by way of a projection and the first and/or second members beformed of low friction hardwearing material.

[0015] In the magnetic tape cartridge of the present invention, theskirt portion is kept in contact with the continuous wall portion on thereel hub to keep the opening closed even when the brake member is in theretracted position, entrance of dust and dirt into the cartridge casingthrough the opening can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is an exploded perspective view of a magnetic tapecartridge in accordance with a first embodiment of the presentinvention,

[0017]FIG. 2 is a side view of the first member of the brake member,

[0018]FIG. 3 is a side view of the second member of the brake member,

[0019]FIG. 4 is a fragmentary cross-sectional view showing an importantpart of the magnetic tape cartridge of the first embodiment,

[0020]FIG. 5 is a fragmentary cross-sectional view showing amodification of the first embodiment,

[0021]FIG. 6 is a view similar to FIG. 5 but showing anothermodification of the first embodiment,

[0022]FIG. 7 is a cross-sectional view of a magnetic tape cartridge inaccordance with a second embodiment of the present invention in a statewhere the magnetic tape cartridge is not used,

[0023]FIG. 8 is an exploded perspective view showing the reel stoppermechanism of the magnetic tape cartridge,

[0024]FIG. 9 is a fragmentary cross-sectional showing the magnetic tapecartridge in a state where it is used,

[0025]FIG. 10 is a fragmentary cross-sectional showing a modification ofthe magnetic tape cartridge of the second embodiment,

[0026]FIG. 11 is a view similar to FIG. 8 but showing the reel stoppermechanism in a magnetic tape cartridge in accordance with a thirdembodiment of the present invention,

[0027]FIG. 12 is a cross-sectional view of a magnetic tape cartridge inaccordance with a fourth embodiment of the present invention in a statewhere the magnetic tape cartridge is not used,

[0028]FIG. 13 is an exploded perspective view showing the reel stoppermechanism of the magnetic tape cartridge,

[0029]FIG. 14 is a fragmentary cross-sectional showing the magnetic tapecartridge in a state where it is used,

[0030]FIG. 15 is a fragmentary cross-sectional view showing an exampleof the through hole and the push rod employed in the fourth embodiment,

[0031]FIGS. 16A and 16B are fragmentary cross-sectional views showinganother example of the through hole and the push rod employed in thefourth embodiment,

[0032]FIG. 17 is a fragmentary cross-sectional view showing stillanother example of the through hole employed in the fourth embodiment,

[0033]FIG. 18 is a fragmentary cross-sectional view showing stillanother example of the through hole and the push rod employed in thefourth embodiment,

[0034]FIG. 19 is a fragmentary cross-sectional view showing stillanother example of the through hole employed in the fourth embodiment,

[0035]FIGS. 20 and 21 show modifications of the brake release member,

[0036]FIGS. 22A and 22B are cross-sectional views showing modificationsof the shapes of the push rod and the through hole,

[0037]FIGS. 23A and 23B are cross-sectional views showing modificationsof the shapes of the push rod and the through hole,

[0038]FIG. 24 is a cross-sectional view of a magnetic tape cartridge inaccordance with a fifth embodiment of the present invention in a statewhere the magnetic tape cartridge is not used,

[0039]FIG. 25 is an exploded perspective view showing the reel stoppermechanism of the magnetic tape cartridge,

[0040]FIG. 26 is a cross-sectional view of a magnetic tape cartridge inaccordance with a sixth embodiment of the present invention in a statewhere the magnetic tape cartridge is not used, and

[0041]FIG. 27 is an exploded perspective view showing the reel stoppermechanism of the magnetic tape cartridge.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0042] In FIG. 1, a magnetic tape cartridge 1 in accordance with a firstembodiment of the present invention comprises a single reel 4 aroundwhich a magnetic tape 20 is wound and is contained for rotation in acartridge casing 7. The reel 4 is formed by bonding together a lowerreel half 5 and an upper reel half 6 by ultrasonic welding. Thecartridge casing 7 is formed by fastening together upper and lowercasing halves 2 and 3 by screws and the like.

[0043] The lower reel half 5 comprises a cylindrical hub 23 and a flange24 which are integrally molded from synthetic resin. A reel plate 8 formagnetically connecting a drive mechanism of a recording and reproducingsystem is mounted on the outer bottom surface of the hub 23. Further onthe inner bottom surface of the hub 23, is formed a stopper gear 23Awhich is brought into engagement with a brake gear 32A formed on a brakemember 30 to be described later and prevents rotation of the reel 4 whenthe magnetic tape cartridge 1 is not used. The hub 23 is provided withan opening 23B, through which a brake release spindle in the recordingand reproducing system is inserted to push upward the brake member 30.An annular groove 23C in which the brake member 30 is fitted is formedaround the opening 23B.

[0044] The brake member 30 comprises a first member 31 having an annularprotrusion 31A (FIG. 2) which is fitted in annular groove 23C of thereel hub 23 and a second member 32 having an annular protrusion which isprojected downward as shown in FIG. 3. The brake gear 32A is formed onthe lower end face of the annular protrusion of the second member 32. Aprojection 31B is formed on the upper surface of the first member 31 andthe second member 32 rests on the projection 31 as shown in FIG. 4.Further an exposed portion 31C which is exposed outward through theopening 23B of the reel hub 23 as shown in FIG. 4 is formed on the lowersurface of the first member 31. A projection 32B which is like a crossin cross-section and is normally held in a groove 2A which is like across in cross-section and is formed on the inner surface of the uppercasing half 2 is provided on the upper surface of the second member 32.

[0045] The brake member 30 is urged downward by a coiled spring 10fitted on the projection 32B and is positioned in the cartridge casing 8with the annular protrusion 31A of the first member 31 received in theannular groove 32C of the reel hub 23, with the brake gear 32A and thestopper gear 23A in mesh with each other and with the projection 32Breceived in the groove 2A as shown in FIG. 4. The height of the firstmember 31 (the distance between the lower end face of the annularprotrusion 32A and the top of the projection 31B) is set so that thesecond member 32 rests on the projection 31B of the first member 31 andthe brake gear 32A and the stopper gear 23A are in mesh with each otherso long as the second member 32 is in a position as urged by the coiledspring 10. Further the height of the annular protrusion 31A of the firstmember 31 and the depth of the annular groove 23C of the reel hub 23 areset so that the annular protrusion 31A is still in the annular groove23C even if the first member 31 is lifted to its uppermost position. Thefirst member 31 and/or the second member 32 is formed of low friction,hardwearing material such as polyoxymethylene, resin added withmolybdenum or the like.

[0046] In this state, rotation of the reel 4 is prevented by engagementbetween the brake gear 32A and the stopper gear 23A. When the magnetictape cartridge 1 is loaded in the recording and reproducing system, thebrake release spindle of the recording and reproducing system pushesupward the exposed portion 31C of the brake member 30, whereby the firstand second members 31 and 32 of the brake member 30 are moved upwardovercoming the force of the coiled spring 10 and the gears 32A and 23Aare disengaged from each other to permit rotation of the reel 4. At thistime, though the annular protrusion 31A of the first member 31 is movedupward relative to the annular groove 23C of the reel hub 23, theprotrusion 31A is not drawn out of the groove 23C as described above.

[0047] A tape outlet opening 26 through which the magnetic tape 20 isdrawn out is formed in a side wall of the cartridge casing 7. The tapeoutlet opening 26 is closed and opened by a slide door 27 which isslidable in the directions of double-headed arrow A and is urged in theclosing position by a spring not shown.

[0048] A leader pin 21 is fixed to the leading end of the magnetic tape20 and when the magnetic tape cartridge 1 is not used, the magnetic tape20 is entirely wound around the reel 4 with the leader pin 21 held in arecess 28 formed near the tape outlet opening 26.

[0049] When the magnetic tape cartridge 1 is loaded in a recording andreproducing system, the gears 23A and 32A of the hub 23 and the brakemember 30 are disengaged from each other to permit rotation of the reel4 in the manner described above and the drive mechanism of the recordingand reproducing system holds the reel plate 8 under magnetic force androtates the reel 4. At the same time, the slide door 27 is opened andthe leader pin 21 is brought to a predetermined position in a taperunning path, thereby recording or reproduction becomes feasible. Inthis state, since the annular protrusion 31A of the first member 31 isstill in the annular groove 23C, dust cannot enter the cartridge casing7 through the opening 23B of the reel hub 23.

[0050] Since the annular protrusion 31A is fitted in the annular groove23C, the first member 31 is sometimes rotated relative to the secondmember 32 in response to rotation of the reel 4. In this particularembodiment, since the first member 31 is in contact with only at theprojection 31B, sliding resistance is small and generation of weartailings can be reduced. Further since the first member 31 and/or thesecond member 32 is formed of low friction, hardwearing material such aspolyoxymethylene, sliding resistance is smaller and generation of weartailings can be more reduced.

[0051] Though, in the first embodiment described above, the groove 23Cis formed in the reel hub 23 and the protrusion 31A of the first member31 is fitted in the groove 23C, an annular wall portion 23D may beformed around the opening 23B as shown in FIG. 5, and the annularprotrusion 31A may be fitted on the annular wall portion 23D. Otherwisean annular wall portion 23E may be formed around the opening 23B and theannular protrusion 31A may be fitted in the annular wall portion 23E asshown in FIG. 6. In this case, it is preferred that an annular flange23F be provided to project inward from the annular wall portion 23E,thereby preventing the first member 31 from falling down through theopening 23B.

[0052] Further, though, in the first embodiment described above, thefirst member 31 is in abutment against the second member 32 at theprojection 31B formed on the first member 31, such a projection may beformed on the second member 32 or on each of the first and secondmembers 31 and 32.

[0053] A magnetic tape cartridge in accordance with a second embodimentof the present invention will be described with reference to FIGS. 7 to9, hereinbelow.

[0054] In FIG. 7, the magnetic tape cartridge 101 of the secondembodiment comprises a single reel 102 around which a magnetic tape (notshown) is wound and is contained for rotation in a cartridge casing 103.The cartridge casing 103 is formed by fastening together upper and lowercasing halves 131 and 132 by screws and the like. The lower casing half132 is provided with a central opening 132 a. Further the magnetic tapecartridge 101 is provided with a reel stopper means 110 which preventsrotation of the reel 102 when the magnetic tape cartridge 101 is notused and permits rotation of the reel 102 when the magnetic tapecartridge 101 is used.

[0055] The reel 102 comprises a reel hub 121 which is a cylindricalmember having a bottom wall 121 a and doughnut-shaped lower and upperflanges 122 and 123 extending outward from the lower and upper ends ofthe reel hub 121. The reel hub 121 and the lower flange 122 are formedintegrally with each other by molding of synthetic resin and the upperflange 123 is fixed to the reel hub 121, for instance, by ultrasonicwelding. Gear teeth (reel gear) 124 for driving the reel 102 are formedin a circle on the lower surface of the bottom wall 121 a of the reelhub 121 and an annular reel plate 125 of magnetic metal is mounted onthe lower surface of the bottom wall 121 a inside the reel gear 124. Thereel gear 124 and the reel plate 125 are exposed outside through thecentral opening 132 a in the cartridge casing 132. The reel 102 is urgeddownward by an urging member 105 to be described later.

[0056] A reel drive means 111 of a tape drive system comprises a rotaryspindle 112 provided with a drive gear 113 formed on the upper end faceof the rotary spindle 112 and a magnet disposed on the upper end face ofthe same. When the magnetic tape cartridge 101 is loaded in the tapedrive system, the rotary spindle 111 is moved upward toward the magnetictape cartridge 101 and the drive gear 113 is brought into mesh with thereel gear 124 while the magnet attracts the reel plate 125 to hold thedrive gear 113 in mesh with the reel gear 124.

[0057] The reel stopper means 110 comprises a brake member 104 which ismovable up and down away from and toward the reel 102, an urging member105 which urges the brake member 104 toward the reel 102 and a brakerelease member 106 which moves the brake member away from the reel 102.

[0058] As shown in FIG. 8, three through holes 126 are formed in thebottom wall 121 a of the reel hub 121 at regular intervals on a circleto extend through the bottom wall 121 a at the portion where the reelgear 124 is formed. Further three engagement projections 127 are erectedfrom the upper surface of the bottom wall 121 a at regular intervals ona circle in positions angularly spaced from the through holes 126. Thenumber of the through holes 126 and the engagement projections 127 neednot be limited to three but for or more through holes 126 and engagementprojections 127 may be formed. The upper end portion of each engagementprojection 127 is shaped like a gear tooth and may be shaped like aplurality of gear teeth. In FIG. 8, only the bottom wall 121 a of thereel hub 121 is shown as the reel 102.

[0059] The brake member 104 is a substantially disc-like member and isdisposed in the reel hub 121 opposed to the bottom wall 121 a of thereel hub 121. A plurality of gear teeth 141 (stopper gear) are annularlyformed on the lower surface of the brake member 104 and are adapted tobe brought into engagement with the engagement projections 127. Astraight protrusion 142 extends upward from the upper surface of thebrake member 104 and is fitted in a guide groove formed in a guideportion 131 a projecting downward from the inner surface of the uppercasing half 131, whereby the brake member 104 is able to be moved towardand away from-the bottom wall 121 a of the reel hub 121 without rotatingrelative to the reel hub 121. The protrusion 142 and the groove in theguide portion 131 a may be like a cross in cross-section.

[0060] An urging member 105 in the form of a coiled spring compressedbetween the upper surface of the brake member 104 urges the brake member104 toward the operative position where the stopper gear 141 and theengagement projections 127 are engaged with each other to preventrotation of the reel 104.

[0061] The brake release member 106 is disposed between the brake member104 and the bottom wall 121 a of the reel hub 121 to be movable up anddown. As shown in FIG. 8, the brake release member 106 comprises acentral disc portion 161 and three arms 162 extending radially outwardfrom the central disc portion 161. A rectangular push rod 163 extendsdownward from the free end of each arm 162 and is inserted for up anddown movement into one of the through holes 126 formed in the bottomwall 121 a of the reel hub 121 with its lower end projected into teethportion of the reel gear 124 on the lower surface of the reel hub 121.The engagement projections 127 are positioned between the arms 162.

[0062] In the lowermost position of the brake release member 106 shownin FIG. 7, the lower end face of each push rod 163 is positionedsubstantially flush with the tips of the teeth of the reel gear 124 and,in response to chucking action of the rotary spindle 111 of the tapedrive system for bringing the drive gear 113 into mesh with the reelgear 124, the push rods 163 are pushed upward to move upward the brakerelease member 106 by a predetermined amount, thereby disengaging theengagement projection 127 from the stopper gear 141 to permit rotationof the reel 102 as shown in FIG. 9. Since the push rods 163 are insertedinto the through holes 126 in the reel hub 121, the brake release member106 is rotated integrally with the reel 102.

[0063] The brake member 104 is urged downward by the urging means 105 sothat the lower surface thereof abuts against the upper surface of thebrake release member 106. A spherical projection 164 is formed on theupper surface of the central disc portion 161 coaxially with the axis ofrotation of the brake release member 106, and a recess 143 having acurved bottom is formed on the lower surface of the brake member 104 sothat the tip of the spherical projection 164 abuts against the center ofthe recess 143. Further an annular protrusion 165 is formed on the uppersurface of the brake release member 106 around the spherical projection164 and the lower surface of the brake member 104 abuts against theupper surface of the protrusion 165. Thus the brake member 104 and thebrake release member 106 contact each other over a limited area, wherebythe resistance to rotation of the reel 102 is reduced and generation ofwear tailings can be suppressed.

[0064] As shown in FIG. 8, a plurality of slits 165 a are formed in theannular protrusion 165 at predetermined intervals. Wear tailingsgenerated between the contact surfaces of the brake member 104 and thebrake release member 106 are gathered in the slits 165 a so that thewear tailings are not held between the contact surfaces to promote wear.

[0065] Though, in the embodiment described above, the projection 164 andthe protrusion 165 are formed on the brake release member 106, they maybe formed on the brake member 104. Further only one of the projection164 and the protrusion 165 may be formed. Since the peripheral speedincreases toward the outer periphery of the central disc portion 161, itis preferred that the annular protrusion 165 be formed nearer to thecenter of the disc portion 161.

[0066] In the modification of the second embodiment shown in FIG. 10,the brake release member 106 contacts the brake member 104 at a ball 150which is press-fitted in a recess formed on the upper surface of thebrake release member 106 and is received in a recess 144 formed in thelower surface of the brake member 104. It is preferred that the ball 150be formed hardwearing material such as steel or ceramics.

[0067] It is preferred that at least one of the brake member 104 and thebrake release member 106 be formed of low friction, hardwearingmaterial. For example, the brake member 104 is formed ofpolyoxymethylene while the brake release member 106 is formed ofpolycarbonate resin, polycarbonate resin added with graphite, ABS resin,ABS resin added with graphite, or nylon resin added with molybdenum.

[0068] Further, as clearly shown in FIG. 8, the protrusion 142 extendslong substantially across the upper surface of the brake member 104 andaccordingly the coiled spring 105 fitted on the protrusion 142 is largein diameter. That is, the coiled spring 105 acts on the brake member 104at a portion near the outer periphery of the brake member 104.Accordingly the coiled spring 105 acts on the brake member 104 at aportion near the push rods 163 which are pushed upward by the rotaryspindle 111 of the tape drive system. With this arrangement, deformationof the brake member 104, especially of the arms 162, can be suppressed,whereby the brake member 104 can be smoothly lifted without frictionbetween the outer surface of the push rod 163 and the inner surface ofthe through hole 126. Since the thickness of the brake member 104,especially of the arms 162, is restricted, the brake member 104 is aptto be deformed when the working point at which the coiled spring 105acts on the brake member 104 is remote from the working point at whichthe upward force transmitted from the rotary spindle 111 by way of thepush rods 163 acts on the brake member 104. When the brake member 104 isdeformed, the outer surface of the push rods 163 brought into contactwith the inner surface of the through holes 126 and frictiontherebetween adversely affects the brake release operation.

[0069] A magnetic tape cartridge in accordance with a third embodimentof the present invention will be described with reference to FIG. 11,hereinbelow.

[0070] The magnetic tape cartridge of the third embodiment issubstantially the same as the second embodiment, and accordingly theelements analogous to those in the second embodiment are given the samereference numerals and only the difference from the second embodimentwill be mainly described. FIG. 11 is a view similar to FIG. 8 butshowing the reel stopper mechanism in the third embodiment.

[0071] As shown in FIG. 11, in this embodiment, rotation of the reel 102is prevented by engagement of an external bevel gear 141′ which isformed on the brake member 104 to conically taper toward the reel hub121 and an internal bevel gear 127′ which is formed on the reel hub 121to conically flare toward the brake member 104. The internal bevel gear127′ is partly cut away and the through holes 126 into which the pushrods 163 of the brake release member 106 are inserted are formed at thecutaway portions.

[0072] In this embodiment, since rotation of the reel 102 is preventedby engagement of the conical gears 141′ and 127′ and the former ispressed against the latter by the urging means, the brake member 104 iscentered with respect to the reel hub 121 so that the center of thebrake member 104 is on the axis of rotation of the reel 102 and thegears 141′ and 127′ are engaged with each other under a uniform pressureover the entire periphery thereof, whereby rotation of the reel 102 canbe surely prevented. Further for the same reason, the brake member 104can be lifted keeping the horizontal position by the sphericalprojection 164 when the push rods 163 are pushed downward and the gear141′ can be surely disengaged from the gear 127′ over the entireperiphery thereof.

[0073] Rotation of the reel 102 may be prevented by pressing a highfriction conical surface on the brake member 104 against a high frictionconical surface on the reel hub 121.

[0074] A magnetic tape cartridge in accordance with a fourth embodimentof the present invention will be described, hereinbelow.

[0075] As shown in FIG. 12, the magnetic tape cartridge 201 of thefourth embodiment comprises a single reel 202 around which a magnetictape (not shown) is wound and is contained for rotation in a cartridgecasing 203. The cartridge casing 203 is formed by fastening togetherupper and lower casing halves 231 and 232 by screws and the like. Thelower casing half 232 is provided with a central opening 232 a. Furtherthe magnetic tape cartridge 201 is provided with a reel stopper means210 which prevents rotation of the reel 202 when the magnetic tapecartridge 201 is not used and permits rotation of the reel 202 when themagnetic tape cartridge 201 is used.

[0076] The reel 202 comprises a reel hub 221 which is a cylindricalmember having a bottom wall 221 a and doughnut-shaped lower and upperflanges 222 and 223 extending outward from the lower and upper ends ofthe reel hub 221. The reel hub 221 and the lower flange 222 are formedintegrally with each other by molding of synthetic resin and the upperflange 223 is fixed to the reel hub 221, for instance, by ultrasonicwelding. Gear teeth (reel gear) 224 for driving the reel 202 are formedin a circle on the lower surface of the bottom wall 221 a of the reelhub 221 and an annular reel plate 225 of magnetic metal is mounted onthe lower surface of the bottom wall 221 a inside the reel gear 224. Thereel gear 224 and the reel plate 225 are exposed outside through thecentral opening 232 a in the cartridge casing 232. The reel 202 is urgeddownward by an urging member 205 to be described later.

[0077] When the magnetic tape cartridge 201 is loaded in the tape drivesystem, the rotary spindle 111 is moved upward toward the magnetic tapecartridge 201 and the drive gear 113 is brought into mesh with the reelgear 224 while the magnet attracts the reel plate 225 to hold the drivegear 113 in mesh with the reel gear 224.

[0078] The reel stopper means 210 comprises a brake member 204 which ismovable up and down away from and toward the reel 202, an urging member205 which urges the brake member 204 toward the reel 202 and a brakerelease member 206 which moves the brake member 204 away from the reel202.

[0079] As shown in FIG. 13, three through holes 226 are formed in thebottom wall 221 a of the reel hub 221 at regular intervals on a circleto extend through the bottom wall 221 a at the portion where the reelgear 224 is formed. Further three engagement projections 227 are erectedfrom the upper surface of the bottom wall 221 a at regular intervals ona circle in positions angularly spaced from the through holes 226. InFIG. 13, only the bottom wall 221 a of the reel hub 221 is shown as thereel 202.

[0080] The brake member 204 comprises a disc-like member 241 disposed inthe reel hub 221 opposed to the bottom wall 221 a of the reel hub 221. Aplurality of gear teeth 242 (stopper gear) are annularly formed on thelower surface of the disc-like member 241 and are adapted to be broughtinto engagement with the engagement projections 227. The lower surfaceof the disc-like member 241 is bulged downward at a central portionthereof and the central portion is brought into abutment against thecentral portion of the upper surface of a central disc portion (to bedescribed later) of the brake release member 206.

[0081] A protrusion 244 extends upward from the upper surface of thedisc-like member 241 of the brake member 204 and an engagement groove245 shaped like a cross in cross-section is formed in the protrusion244. An engagement projection 233 projecting downward from the innersurface of the upper casing half 231 is inserted into the engagementgroove 245, whereby the brake member 204 is able to be moved toward andaway from the bottom wall 221 a of the reel hub 221 without rotatingrelative to the reel hub 221.

[0082] An urging member 205 in the form of a coiled spring compressedbetween the upper surface of the brake member 204 urges the brake member204 toward the operative position where the stopper gear 242 and theengagement projections 227 are engaged with each other to preventrotation of the reel 204.

[0083] The brake release member 206 is disposed between the brake member204 and the bottom wall 221 a of the reel hub 221 to be movable up anddown. As shown in FIG. 13, the brake release member 206 comprises acentral disc portion 261 and three arms 262 extending radially outwardfrom the central disc portion 261. A rectangular push rod 263 extendsdownward from the free end of each arm 262 and is inserted for up anddown movement into one of the through holes 226 formed in the bottomwall 221 a of the reel hub 221 with its lower end projected into teethportion of the reel gear 224 on the lower surface of the reel hub 221.The engagement projections 227 are positioned between the arms 262. Thepush rod 263 may be circular or ellipsoidal in cross-section. The brakerelease member 206 may be shaped like a triangle with the push rods 263formed to extend downward at the corners of the triangle.

[0084] In the lowermost position of the brake release member 206 shownin FIG. 12, the lower end face of each push rod 263 is positionedsubstantially flush with the tips of the teeth of the reel gear 224 and,in response to chucking action of the rotary spindle 111 of the tapedrive system for bringing the drive gear 113 into mesh with the reelgear 224, the push rods 263 are pushed upward to move upward the brakerelease member 206 by a predetermined amount, thereby disengaging theengagement projection 227 from the stopper gear 241 to permit rotationof the reel 202 as shown in FIG. 14. Since the push rods 263 areinserted into the through holes 226 in the reel hub 221, the brakerelease member 206 is rotated integrally with the reel 202.

[0085] The brake member 204 is urged downward by the urging means 205 sothat the bulged central portion of the lower surface thereof is insliding contact with the upper surface of the brake release member 206.

[0086] Each of the through holes 226 formed in the reel hub 221 opensdownward at the portion of the lower surface of the reel hub 221 atwhich the reel gear 224 is formed in an area including at least a pairof opposed flanks of the reel gear 221 which form a valley of the reelgear 224. The through hole 226 may be of a rectangle, circle orellipsoid or the like according to the cross-sectional shape of the pushrod 263.

[0087] For example, as shown in FIG. 15, the through hole 226 opens in awidth of one pitch of the reel gear 224 by cutting away a pair of flanks224 a between the tips 224 a of a pair of adjacent teeth. In thisexample, the opposed flanks 224 a are inclined at the same angle and thecenter of the push rod 263 coincides with the center of the valleyformed by the flanks 224 a and with the tip of a tooth of the drive gear113 in mesh with the reel gear 224.

[0088] The through hole 226 should cover at least one valley and wheneach valley of the reel gear 224 is small because of a small diameter ofthe reel gear 224 or a small number of teeth, the through hole 226 isextended on one side or opposite sides of the valley as shown in FIGS.18 and 19 to be described later.

[0089] With this arrangement, even if the phase of the drive gear 113 isshifted from the phase of the reel gear 224 within one pitch when theformer is brought into mesh with the latter, the tip of a tooth of thedrive gear 113 can be surely brought into abutment against the lower endface of the push rod 263, whereby the push rod 263 can be surely liftedto disengage the stopper gear 242 from the engagement projections 227.

[0090] A recess 263 a which is adapted to be engaged with the tip of atooth of the drive gear 113 may be formed on the lower surface of thepush rod 263 as shown in FIGS. 16A and 16B.

[0091] The tips 224 a of the teeth on opposite sides of the through hole226 may be cut flat at shown in FIG. 17. Otherwise such tips may berounded or chamfered.

[0092] With this arrangement, generation of sharp edges by cutting awaya part of the reel gear 224 can be avoided, which facilitates formationof the mold for molding the reel hub 221 and facilitates molding of thereel hub 221.

[0093] In the modification shown in FIG. 18, the through hole 226 iswider than one pitch of the reel gear 224 and is formed by cutting awaya pair of adjacent teeth from the root thereof with a pair of flatsurfaces 24 c formed on opposite sides of the through hole 226.

[0094] In the modification shown in FIG. 19, the tip 224 a of each toothof the reel gear 224 is flat on the outer portion and sharp on the innerportion and the height of the tooth becomes smaller toward the innerperiphery. Further the inclinations of the flanks on opposite sides ofeach valley differ from each other. The through hole 226 is wider thanone pitch of the reel gear 224 and is formed by cutting away a pair ofadjacent teeth from the root thereof with a pair of flat surfaces 24 cformed on opposite sides of the through hole 226.

[0095]FIGS. 20 and 21 show modifications of the brake release member206. In these modifications, a blank in the form of a development of thebrake release member 206 is stamped out from a sheet metal and the blankis bent into the brake release member 206. In the modification shown inFIG. 20, the blank has push rod portions extending in the longitudinaldirection of the portions forming the arms 262 and the push rod portionsare bent downward by 900 to form the push rods 263. The tip portion ofeach of the push rod portions is further bent to form an abutmentportion 263 b on the lower end of the push rod 263. In the modificationshown in FIG. 21, the blank has push rod portions extending laterallyfrom the ends of the portions forming the arms 262 and the push rodportions are bent downward by 90° to form the push rods 263. The tipportion of each of the push rod portions is further bent to form anabutment portion 263 b on the lower end of the push rod 263.

[0096] By thus forming the brake release member 206 of sheet metal, thebrake release member 206 can be sufficiently rigid for its thickness.

[0097] It is preferred that the push rod 263 be arranged so that thepush rod 263 contacts with the inner surface of the through hole 226 atfine protrusions formed on the outer surface of the push rod 263 or onthe inner surface of the through hole 226 to extend in the longitudinaldirection of the push rod 263 in order to reduce the contact areatherebetween.

[0098] In the example shown in FIG. 22A, the push rod 263 is square incross-section and a plurality of protrusions 226 a are formed on theinner surface of the through hole 226 to extend in the longitudinaldirection of the push rod 263, whereby the push rod 263 contacts withthe inner surface of the through hole 226 only at the protrusions 226 a.In the example shown in FIG. 22B, a plurality of protrusions 263 d areformed on the outer surface of the push rod 263 to extend in thelongitudinal direction of the push rod 263.

[0099] In the examples shown in FIGS. 23A and 23B, the push rod 263 iscircular in cross-section, a plurality of protrusions 226 a are formedon the inner surface of the through holes 226.

[0100] In the examples shown in FIGS. 22A, 22B, 23A and 23B, theprotrusions 226 a and 263 d are about several tens μm though exaggeratedin the drawings.

[0101] A magnetic tape cartridge 301 in accordance with a fifthembodiment of the present invention will be described with reference toFIGS. 24 and 25, hereinbelow. The magnetic tape cartridge 301 of thisembodiment differs from that of the second embodiment mainly in thestructure of the reel stopper means, and accordingly only the structureof the reel stopper means will be mainly described.

[0102] As shown in FIGS. 24 and 25, in this embodiment, the reel stoppermeans 310 comprises a brake member 304 which is movable up and down awayfrom and toward the reel 302, an urging member 305 which is formedintegrally with the brake member 304 and urges the brake member 304toward the reel 302 and a brake release member 306 which moves the brakemember away from the reel 302.

[0103] As shown in FIG. 25, three through holes 326 are formed in thebottom wall 321 a of the reel hub 321 at regular intervals on a circleto extend through the bottom wall 321 a at the portion where the reelgear 324 is formed. Further three engagement projections 327 are erectedfrom the upper surface of the bottom wall 321 a at regular intervals ona circle in positions angularly spaced from the through holes 326. Theupper end portion of each engagement projection 327 is tapered. In FIG.8, only the bottom wall 321 a of the reel hub 321 is shown as the reel302.

[0104] The brake member 304 is formed by a plate material and has acentral disc portion 341 convex upward and concave downward and threearms 342 extending radially outward from the disc portion 341. The freeend portion of each arm 342 is bent downward to form a pair ofengagement portions 343 which forms an engagement recess in which thetip of the engagement projection 327 is fitted to prevent rotation ofthe reel 302. Three spring plates 305 extend radially outward from thedisc portion 341 between the arms 342.

[0105] An annular holding portion 333 extends downward from the innersurface of the upper casing half 331. Three first recesses 333 a areformed on the lower end face of the holding portion 333 at regularintervals and three second recesses 333 b are formed on the lower endface of the holding portion 333 between the first recesses 333 a. Thefirst recesses 333 a are deeper than the second recesses 333 b and thefree end portions of the arms 342 are inserted into the first recesses333 a to be movable up and down. The free end portions of the platesprings 305 are engaged in the second recesses 333 b.

[0106] With this arrangement, the brake member 304 is able to be movedtoward and away from the bottom wall 321 a of the reel hub 321 withoutrotating relative to the reel hub 321, and is urged toward the reel hub304 by the plate springs 305.

[0107] The brake release member 306 is disposed between the brake member304 and the bottom wall 321 a of the reel hub 321 to be movable up anddown. As shown in FIG. 25, the brake release member 306 comprises acentral disc portion 361 and three arms 362 extending radially outwardfrom the central disc portion 361. A rectangular push rod 363 extendsdownward from the free end of each arm 362 and is inserted for up anddown movement into one of the through holes 326 formed in the bottomwall 321 a of the reel hub 321 with its lower end projected into teethportion of the reel gear 324 on the lower surface of the reel hub 321.The engagement projections 327 are positioned between the arms 362.

[0108] A spherical projection 364 is formed on the upper surface of thecentral disc portion 361 and is in contact with the lower concavesurface of the central disc portion 341.

[0109] In the lowermost position of the brake release member 306 shownin FIG. 24, the lower end face of each push rod 363 is positionedsubstantially flush with the tips of the teeth of the reel gear 324 and,in response to chucking action of the rotary spindle 111 of the tapedrive system for bringing the drive gear 113 into mesh with the reelgear 324, the push rods 363 are pushed upward to move upward the brakerelease member 306 by a predetermined amount, thereby disengaging theengagement projection 327 from the engagement portions 343 to permitrotation of the reel 302. Since the push rods 363 are inserted into thethrough holes 326 in the reel hub 321, the brake release member 306 isrotated integrally with the reel 302.

[0110] In this embodiment, since the brake member 304 and the urgingmeans 305 are integral with each other, the number of parts can bereduced and assembly of the magnetic tape cartridge is facilitated.

[0111] A magnetic tape cartridge 401 in accordance with a sixthembodiment of the present invention will be described with reference toFIGS. 26 and 27, hereinbelow. The magnetic tape cartridge 401 of thisembodiment differs from that of the second embodiment mainly in thestructure of the reel stopper means, and accordingly only the structureof the reel stopper means will be mainly described.

[0112] As shown in FIGS. 26 and 27, in this embodiment, the reel stoppermeans 410 comprises a brake release member 404 which is rotatableintegrally with the reel 402 and is movable up and down away in responseto chucking operation of the rotary spindle 111 of the tape drivesystem, a brake member 405 which is fixed to the cartridge casing 403and is brought into engagement with a part of the brake release member404 to prevent rotation of the reel 402, and urging members 406 whichurges the brake release member 404 toward the position where it engageswith the brake member 405.

[0113] As shown in FIG. 27, three through holes 426 are formed in thebottom wall 421 a of the reel hub 421 at regular intervals on a circleto extend through the bottom wall 421 a at the portion where the reelgear 424 is formed. Further three spring retainer projections 427 areformed on the inner peripheral surface of the reel hub 421 at regularintervals in positions angularly spaced from the through holes 426 asshown in FIG. 26. Each spring retainer portion 427 is provided with arecess into which the base portion of a plate spring 406 (urging member)is inserted as will be described later. In FIG. 27, only the bottom wall421 a of the reel hub 421 is shown as the reel 402.

[0114] The brake member 405 comprises a disc portion 451. A stopper gear452 is formed on the upper surface of the disc portion 451 along theouter periphery thereof and a projection 453 extends upward at thecentral portion of the disc portion 451. The projection 453 is fixed inan annular recess 431 a formed on the inner surface of the upper casinghalf 431, whereby the brake member 405 is fixed to the cartridge casing403 not to be rotatable. The brake member 405 is disposed inside thereel hub 421 opposed to the bottom wall 421 a thereof.

[0115] The brake release member 404 comprising an annular portion 441provided with a central opening. A brake gear 442 (FIG. 26) which isadapted to be engaged with the stopper gear 452 is formed on the lowersurface of the annular portion 441. The brake release member 404 isdisposed above the brake member 405 to be movable up and down with theprojection 453 of the brake member 405 extending through the centralopening of the annular portion 441. Three rectangular push rods 443extend downward from the outer periphery of the annular portion 441 andare inserted for up and down movement into the through holes 426 formedin the bottom wall 421 a of the reel hub 421 with its lower endprojected into teeth portion of the reel gear 424 on the lower surfaceof the reel hub 421.

[0116] Each of the plate springs 406 comprises a vertical base portionand a curved resilient arm portion. The plate spring 406 is mounted onthe reel hub 421 by inserting the base portion into the spring retainerportion 427 with the resilient arm portion in abutment against the uppersurface of the annular portion 441 of the brake release member 404.

[0117] In the lowermost position of the brake release member 404 shownin FIG. 26, the lower end face of each push rod 443 is positionedsubstantially flush with the tips of the teeth of the reel gear 424 and,in response to chucking action of the rotary spindle 111 of the tapedrive system for bringing the drive gear 113 into mesh with the reelgear 424, the push rods 443 are pushed upward to move upward the brakerelease member 404 by a predetermined amount, thereby disengaging thestopper gear 452 from the brake gear 442 to permit rotation of the reel402. Since the push rods 443 are inserted into the through holes 426 inthe reel hub 421, the brake release member 404 is rotated integrallywith the reel 402. In this embodiment, since the brake release member404 is rotated without contacting the brake member 405, resistance torotation of the reel 402 is reduced and generation of wear tailings isprevented.

[0118] In the embodiments described above, it is preferred that thebrake release member be formed of fiber reinforced resin such aslong-fiber reinforced resin, carbon fiber reinforced resin and the like.Such fiber reinforced resin comprises polyamide resin, polyoxymethylene,polycarbonate, ABS resin, polybutylene terephthalate and the like addedwith glass fiber, carbon fiber, boron fiber, silicon carbide fiber,alumina fiber and the like.

[0119] Further it is preferred that the brake member and/or the brakerelease member be formed of synthetic resin containing therein lubricantsuch as molybdenum, polytetrafluoroethylene, graphite, potassiumtitanate whisker, silicone formed of dimethyl polysiloxane of variousgrades and modifications thereof and the like.

[0120] In addition to the lubricant listed above, amide oleatelubricant, ercuamide lubricant, amide stearate lubricant, bis-aliphaticacid lubricant, nonionic surface active agent lubricant, hydrocarbonlubricant, aliphatic acid lubricant, ester lubricant, alcohol lubricant,metal soap and the like may be added.

[0121] As the synthetic resin, polycarbonate, polyoxymethylene, PPS,aliphatic polyamide such as nylon 6, nylon 66(6,6;6/6) and the like,aromatic polyamide, ultra-high-molecular-weight polyethylene, isotacticpolypropylene, syndiotactic polystyrene, and hard-wearing resin havingan imide group such as polyimide, polyamideimide, polyether imide andthe like are preferred.

What is claimed is:
 1. A magnetic tape cartridge comprising a cartridgecasing, a single reel around which a magnetic tape is wound and which iscontained in the cartridge casing for rotation, the reel having a reelhub in the form of a cylindrical member which has a bottom wall and isprovided with an opening and a stopper gear formed on the bottom wall,and a brake means which is provided with a brake gear and is movable upand down between an operative position where the brake gear is broughtinto engagement with the stopper gear to prevent rotation of the reeland a retracted position where the brake gear is disengaged from thestopper gear to permit rotation of the reel, the brake means beingnormally urged toward the operative position and moved to the retractedposition by a pusher member of a tape drive system which acts on thebrake means through the opening in the reel hub when the magnetic tapecartridge is loaded in the tape drive system, wherein the improvementcomprises that a continuous wall portion is erected around the openingin the reel hub, and the brake means comprises a horizontal portionwhich is disposed above the opening in the reel hub and receives forcefrom the pusher member when the brake means is moved to the retractedposition and a continuous skirt portion which extends downward from thehorizontal portion and is in contact with the continuous wall portion ofthe reel hub, thereby closing the opening together with the horizontalportion, the brake means being moved between the operative position andthe retracted position with the skirt portion kept in contact with thecontinuous wall portion of the reel hub.
 2. A magnetic tape cartridge asdefined in claim 1 in which the brake means comprises a first member anda second member which abuts against the first member and is movable upand down together with the first member, said horizontal portion and theskirt portion are formed on the first member and the brake means isurged toward the operative position by a spring means which acts on thesecond member.
 3. A magnetic tape cartridge as defined in claim 2 inwhich the skirt portion is fitted on the continuous wall portion.
 4. Amagnetic tape cartridge as defined in claim 2 in which the skirt portionis fitted in the continuous wall portion.
 5. A magnetic tape cartridgeas defined in claim 2 in which the first and second members abut againsteach other by way of a projection.
 6. A magnetic tape cartridge asdefined in claim 2 in which at least one of the first and second membersis formed of low friction hardwearing material.
 7. A magnetic tapecartridge as defined in claim 6 in which the first member is formed offiber reinforced resin such as long-fiber reinforced resin, carbon fiberreinforced resin and the like.
 8. A magnetic tape cartridge as definedin claim 6 in which at least one of the first and second members isformed of synthetic resin containing therein lubricant selected from thegroup consisting of molybdenum, polytetrafluoroethylene, graphite,potassium titanate whisker, and silicone formed of dimethyl polysiloxaneof various grades and modifications thereof.
 9. A magnetic tapecartridge as defined in claim 6 in which at least one of the first andsecond members is formed of polyoxymethylene resin added withmolybdenum.
 10. A magnetic tape cartridge comprising a cartridge casing,a single reel around which a magnetic tape is wound and which iscontained in the cartridge casing for rotation, and a brake means whichis movable between an operative position where it prevents rotation ofthe reel and a retracted position where it permits rotation of the reel,wherein the improvement comprises that the brake means comprises a brakemember which is disposed in the cartridge casing not to be rotatable andis movable between an operative position where it engages with the reelto prevent rotation of the reel and a retracted position where it isdisengaged from the reel to permit rotation of the reel, an urging meanswhich urges the brake member toward the operative position, and a brakerelease member which is disposed in the cartridge casing to be rotatedtogether with the reel and moves the brake member to the retractedposition in response to chucking operation of a tape drive mechanism ofa tape drive system, the brake release member being in sliding contactwith the brake member by way of a projection.
 11. A magnetic tapecartridge as defined in claim 10 in which the brake release member is insliding contact with the brake member by way of a ball.
 12. A magnetictape cartridge as defined in claim 10 in which the brake release memberis in sliding contact with the brake member by way of a sphericalprojection formed on the axis of rotation of the brake release member.13. A magnetic tape cartridge as defined in claim 10 in which the brakerelease member is in sliding contact with the brake member by way of anannular protrusion.
 14. A magnetic tape cartridge as defined in claim 10in which the brake release member is formed of fiber reinforced resinsuch as long-fiber reinforced resin, carbon fiber reinforced resin andthe like.
 15. A magnetic tape cartridge as defined in claim 10 in whichat least one of the brake release member and the brake member is formedof synthetic resin containing therein lubricant selected from the groupconsisting of molybdenum, polytetrafluoroethylene, graphite, potassiumtitanate whisker, and silicone formed of dimethyl polysiloxane ofvarious grades and modifications thereof.
 16. A magnetic tape cartridgecomprising a cartridge casing, a single reel around which a magnetictape is wound and which is contained in the cartridge casing forrotation, and a brake means which is movable between an operativeposition where it prevents rotation of the reel and a retracted positionwhere it permits rotation of the reel, wherein the improvement comprisesthat the brake means comprises a brake member which is disposed in thecartridge casing not to be rotatable and is movable between an operativeposition where it engages with the reel to 20 prevent rotation of thereel and a retracted position where it is disengaged from the reel topermit rotation of the reel, an urging means which urges the brakemember toward the operative position, and a brake release member whichis disposed in the cartridge casing to be rotated togther with the reeland moves the brake member to the retracted position in response tochucking operation of a tape drive mechanism of a tape drive system,said brake member having an engagement surface which is conicallyinclined with respect to the axis of rotation of the reel and is broughtinto engagement with a complementary surface formed on the reel toprevent rotation of the reel when the brake member is moved to theoperative position.
 17. A magnetic tape cartridge as defined in claim 16in which the brake release member is formed of fiber reinforced resinsuch as long-fiber reinforced resin, carbon fiber reinforced resin andthe like.
 18. A magnetic tape cartridge as defined in claim 16 in whichat least one of the brake release member and the brake member is formedof synthetic resin containing therein lubricant selected from the groupconsisting of molybdenum, polytetrafluoroethylene, graphite, potassiumtitanate whisker, and silicone formed of dimethyl polysiloxane ofvarious grades and modifications thereof.
 19. A magnetic tape cartridgecomprising a cartridge casing, a single reel around which a magnetictape is wound and which is contained in the cartridge casing forrotation, and a brake means which is movable between an operativeposition where it prevents rotation of the reel and a retracted positionwhere it permits rotation of the reel, wherein the improvement comprisesthat the brake means comprises a brake member which is movable betweenan operative position where it engages with the reel to prevent rotationof the reel and a retracted position where it is disengaged from thereel to permit rotation of the reel, an urging means which urges thebrake member toward the operative position, and a brake release memberwhich is disposed in the cartridge casing to be rotated together withthe reel and moves the brake member to the retracted position inresponse to chucking operation of a tape drive mechanism of a tape drivesystem, said urging means acting on the brake member in a position nearthe position where the tape drive mechanism acts on the brake releasemember to move the brake member to the retracted position.
 20. Amagnetic tape cartridge as defined in claim 19 in which said urgingmeans acts on the brake member in a position opposed to the positionwhere the brake member is engaged with the reel to prevent rotation ofthe reel.
 21. A magnetic tape cartridge as defined in claim 19 in whichthe brake release member is formed of fiber reinforced resin such aslong-fiber reinforced resin, carbon fiber reinforced resin and the like.22. A magnetic tape cartridge as defined in claim 19 in which at leastone of the brake release member and the brake member is formed ofsynthetic resin containing therein lubricant selected from the groupconsisting of molybdenum, polytetrafluoroethylene, graphite, potassiumtitanate whisker, and silicone formed of dimethyl polysiloxane ofvarious grades and modifications thereof.
 23. A magnetic tape cartridgecomprising a cartridge casing, a single reel around which a magnetictape is wound and which is contained in the cartridge casing forrotation, and a brake means which is movable between an operativeposition where it prevents rotation of the reel and a retracted positionwhere it permits rotation of the reel, wherein the improvement comprisesthat the brake means comprises a brake member which is movable betweenan operative position where it engages with the reel to prevent rotationof the reel and a retracted position where it is disengaged from thereel to permit rotation of the reel, an urging means which urges thebrake member toward the operative position, and a brake release memberwhich is disposed in the cartridge casing to be rotated together withthe reel and moves the brake member to the retracted position inresponse to chucking operation of a tape drive mechanism of a tape drivesystem, the reel is provided with a reel gear which is brought into meshwith a drive gear of the tape drive mechanism and a through hole throughwhich a push rod extending from the brake release member projects to bebrought into abutment against the drive gear of the tape drive mechanismso that the brake release member moves the brake member to the retractedposition, and the through hole opens in an area including at least apair of opposed flanks of the reel gear which form a valley of the reelgear.
 24. A magnetic tape cartridge as defined in claim 23 in which thethrough hole opens between the tips of adjacent teeth of the reel gear.25. A magnetic tape cartridge as defined in claim 23 in which thethrough hole is formed by cutting away two or more teeth of the reelgear.
 26. A magnetic tape cartridge as defined in claim 23 in which arecess which is able to be engaged with the tip of the drive gear isformed on the end face of the push rod.
 27. A magnetic tape cartridge asdefined in claim 23 in which the brake release member is formed of fiberreinforced resin such as long-fiber reinforced resin, carbon fiberreinforced resin and the like.
 28. A magnetic tape cartridge as definedin claim 23 in which at least one of the brake release member and thebrake member is formed of synthetic resin containing therein lubricantselected from the group consisting of molybdenum,polytetrafluoroethylene, graphite, potassium titanate whisker, andsilicone formed of dimethyl polysiloxane of various grades andmodifications thereof.
 29. A magnetic tape cartridge as defined in claim23 in which the brake release member is formed by stamping out adevelopment of the brake release member from a sheet metal and bendingthe development into the brake release member.
 30. A magnetic tapecartridge comprising a cartridge casing, a single reel around which amagnetic tape is wound and which is contained in the cartridge casingfor rotation, and a brake means which is movable between an operativeposition where it prevents rotation of the reel and a retracted positionwhere it permits rotation of the reel, wherein the improvement comprisesthat the brake means comprises a brake member which is movable betweenan operative position where it engages with the reel to prevent rotationof the reel and a retracted position where it is disengaged from thereel to permit rotation of the reel, an urging means which urges thebrake member toward the operative position, and a brake release memberwhich is disposed in the cartridge casing to be rotated together withthe reel and moves the brake member to the retracted position inresponse to chucking operation of a tape drive mechanism of a tape drivesystem, the reel is provided with a reel gear which is brought into meshwith a drive gear of the tape drive mechanism and a through hole throughwhich a push rod extending from the brake release member projects to bebrought into abutment against the drive gear of the tape drive mechanismso that the brake release member moves the brake member to the retractedposition, and the push rod and the through hole are in contact with eachother by way of fine protrusions formed at least one of the push rod andthe through hole.
 31. A magnetic tape cartridge as defined in claim 30in which the brake release member is formed of fiber reinforced resinsuch as long-fiber reinforced resin, carbon fiber reinforced resin andthe like.
 32. A magnetic tape cartridge as defined in claim 30 in whichat least one of the brake release member and the brake member is formedof synthetic resin containing therein lubricant selected from the groupconsisting of molybdenum, polytetrafluoroethylene, graphite, potassiumtitanate whisker, and silicone formed of dimethyl polysiloxane ofvarious grades and modifications thereof.
 33. A magnetic tape cartridgecomprising a cartridge casing, a single reel around which a magnetictape is wound and which is contained in the cartridge casing forrotation, and a brake means which is movable between an operativeposition where it prevents rotation of the reel and a retracted positionwhere it permits rotation of the reel, wherein the improvement comprisesthat the brake means comprises a brake member which is movable betweenan operative position where it engages with the reel to prevent rotationof the reel and a retracted position where it is disengaged from thereel to permit rotation of the reel, an urging means which urges thebrake member toward the operative position, and a brake release memberwhich is disposed in the cartridge casing to be rotated together withthe reel and moves the brake member to the retracted position inresponse to chucking operation of a tape drive mechanism of a tape drivesystem, the brake member and the urging means being formed integrallywith each other.
 34. A magnetic tape cartridge as defined in claim 33 inwhich said urging means comprises a plate spring formed integrally withthe brake member.
 35. A magnetic tape cartridge as defined in claim 33in which the brake release member is formed of fiber reinforced resinsuch as long-fiber reinforced resin, carbon fiber reinforced resin andthe like.
 36. A magnetic tape cartridge as defined in claim 33 in whichat least one of the brake release member and the brake member is formedof synthetic resin containing therein lubricant selected from the groupconsisting of molybdenum, polytetrafluoroethylene, graphite, potassiumtitanate whisker, and silicone formed of dimethyl polysiloxane ofvarious grades and modifications thereof.
 37. A magnetic tape cartridgecomprising a cartridge casing, a single reel around which a magnetictape is wound and which is contained in the cartridge casing forrotation, and a brake means which is movable between an operativeposition where it prevents rotation of the reel and a retracted positionwhere it permits rotation of the reel, wherein the improvement comprisesthat the brake means comprises a brake member which is movable betweenan operative position where it engages with the reel to prevent rotationof the reel and a retracted position where it is disengaged from thereel to permit rotation of the reel, an urging means which urges thebrake member toward the operative position, and a brake release memberwhich is disposed in the cartridge casing to be rotated together withthe reel and moves the brake member to the retracted position inresponse to chucking operation of a tape drive mechanism of a tape drivesystem, the urging means being in the form of a plate spring which isfixed to the reel at one end and is in abutment against the brakerelease member at the other end.
 38. A magnetic tape cartridge asdefined in claim 37 in which the brake release member is formed of fiberreinforced resin such as long-fiber reinforced resin, carbon fiberreinforced resin and the like.
 39. A magnetic tape cartridge as definedin claim 37 in which at least one of the brake release member and thebrake member is formed of synthetic resin containing therein lubricantselected from the group consisting of molybdenum,polytetrafluoroethylene, graphite, potassium titanate whisker, andsilicone formed of dimethyl polysiloxane of various grades andmodifications thereof.